Expandable sheath for introducing an endovascular delivery device into a body

ABSTRACT

Embodiments of an expandable sheath can be used in conjunction with a catheter assembly to introduce a prosthetic device, such as a heart valve, into a patient. Such embodiments can minimize trauma to the vessel by allowing for temporary expansion of a portion of the introducer sheath to accommodate the delivery apparatus, followed by a return to the original diameter once the prosthetic device passes through. Some embodiments can include a sheath with inner and outer layers, where a folded portion of the inner layer extends through a slit in the outer layer and a portion of the outer layer overlaps the folded portion of the inner layer. Some embodiments include an elastic outer cover positioned outside the outer layer. Embodiments of the present expandable sheath can avoid the need for multiple insertions for the dilation of the vessel, thus offering advantages over prior art introducer sheaths.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 14/324,894, filed Jul. 7, 2014, which is a continuation of U.S.patent application Ser. No. 13/312,739, filed Dec. 6, 2011, which is acontinuation-in-part of U.S. patent application Ser. No. 12/249,867,filed Oct. 10, 2008, now U.S. Pat. No. 8,690,936; these applications arehereby incorporated by reference herein in their entirety.

FIELD

The present application concerns embodiments of a sheath for use withcatheter-based technologies for repairing and/or replacing heart valves,as well as for delivering a prosthetic device, such as a prostheticvalve to a heart via the patient's vasculature.

BACKGROUND

Endovascular delivery catheter assemblies are used to implant prostheticdevices, such as a prosthetic valve, at locations inside the body thatare not readily accessible by surgery or where access without invasivesurgery is desirable. For example, aortic, mitral, tricuspid, and/orpulmonary prosthetic valves can be delivered to a treatment site usingminimally invasive surgical techniques.

An introducer sheath can be used to safely introduce a deliveryapparatus into a patient's vasculature (e.g., the femoral artery). Anintroducer sheath generally has an elongated sleeve that is insertedinto the vasculature and a housing that contains one or more sealingvalves that allow a delivery apparatus to be placed in fluidcommunication with the vasculature with minimal blood loss. Aconventional introducer sheath typically requires a tubular loader to beinserted through the seals in the housing to provide an unobstructedpath through the housing for a valve mounted on a balloon catheter. Aconventional loader extends from the proximal end of the introducersheath, and therefore decreases the available working length of thedelivery apparatus that can be inserted through the sheath and into thebody.

Conventional methods of accessing a vessel, such as a femoral artery,prior to introducing the delivery system include dilating the vesselusing multiple dilators or sheaths that progressively increase indiameter. This repeated insertion and vessel dilation can increase theamount of time the procedure takes, as well as the risk of damage to thevessel.

Radially expanding intravascular sheaths have been disclosed. Suchsheaths tend to have complex mechanisms, such as ratcheting mechanismsthat maintain the shaft or sheath in an expanded configuration once adevice with a larger diameter than the sheath's original diameter isintroduced.

However, delivery and/or removal of prosthetic devices and othermaterial to or from a patient still poses a significant risk to thepatient. Furthermore, accessing the vessel remains a challenge due tothe relatively large profile of the delivery system that can causelongitudinal and radial tearing of the vessel during insertion. Thedelivery system can additionally dislodge calcified plaque within thevessels, posing an additional risk of clots caused by the dislodgedplaque.

Accordingly, there remains a need in the art for an improved introducersheath for endovascular systems used for implanting valves and otherprosthetic devices.

SUMMARY

Embodiments of the present expandable sheath can minimize trauma to thevessel by allowing for temporary expansion of a portion of theintroducer sheath to accommodate a delivery system, followed by a returnto the original diameter once the delivery system passes through. Someembodiments can comprise a sheath with a smaller profile than that ofprior art introducer sheaths. Furthermore, certain embodiments canreduce the length of time a procedure takes, as well as reduce the riskof a longitudinal or radial vessel tear, or plaque dislodgement becauseonly one sheath is required, rather than several different sizes ofsheaths. Embodiments of the present expandable sheath can require only asingle vessel insertion, as opposed to requiring multiple insertions forthe dilation of the vessel.

One embodiment of a sheath for introducing a prosthetic device comprisesan inner layer and an outer layer. At least a portion of the sheath canbe designed or configured to locally expand from a first diameter to asecond diameter as the prosthetic device is pushed through a lumen ofthe sheath, and then at least partially return to the first diameteronce the prosthetic device has passed through. Some embodiments canadditionally include an elastic outer cover disposed about the outerlayer.

The inner layer can comprise polytetrafluoroethylene (PTFE), polyimide,polyetheretherketone (PEEK), polyurethane, nylon, polyethylene,polyamide, or combinations thereof. The outer layer can comprise PTFE,polyimide, PEEK, polyurethane, nylon, polyethylene, polyamide, polyetherblock amides, polyether block ester copolymer, thermoset silicone,latex, poly-isoprene rubbers, high density polyethylene (HDPE),Tecoflex, or combinations thereof. In one exemplary embodiment, theinner layer can comprise PTFE and the outer layer can comprise acombination of HDPE and Tecoflex. If present, the elastic outer covercan include any suitable materials, such as any suitable heat shrinkmaterials. Examples include Pebax, polyurethane, silicone, and/orpolyisoprene.

Disclosed embodiments of a sheath comprise a proximal end and a distalend opposite one another. Some embodiments can include a hemostasisvalve at or near the proximal end of the sheath. In some embodiments,the outer diameter of the sheath decreases along a gradient from theproximal end to the distal end of the sheath. In other embodiments, theouter diameter of the sheath is substantially constant along at least amajority of the length of the sheath.

One embodiment of a sheath for introducing a prosthetic device into abody can comprise a continuous inner layer defining a lumentherethrough, the inner layer having a folded portion and adiscontinuous outer layer having an overlapping portion and anunderlying portion. In some embodiments, the inner layer can have atleast two folded portions. The outer layer can be configured so that theoverlapping portion overlaps the underlying portion, wherein at least aportion of the folded portion of the inner tubular layer is positionedbetween the overlapping and underlying portions. At least a portion ofthe sheath is configured to expand to accommodate the prosthetic device.

In some embodiments, at least a portion of the sheath is configured suchthat a plurality of segments of the sheath each locally expands one at atime from a rest configuration having a first diameter to an expandedconfiguration having a second diameter that is larger than the firstdiameter to facilitate passage of the prosthetic device through thelumen of the inner layer. Each segment can have a length defined alongthe longitudinal axis of the sheath, and each segment of the sheath canbe configured to at least partially return to the first diameter oncethe prosthetic device has passed through. In some embodiments, when eachsegment of the sheath is in the expanded configuration, a length of thefolded portion corresponding to the length of the segment at leastpartially unfolds (e.g., by separating and/or straightening). A lengthof the overlapping portion corresponding to the length of the segmentcan be configured to move with respect to the underlying portion wheneach segment of the sheath expands from the rest configuration to theexpanded configuration.

In one specific embodiment, the inner layer comprises PTFE and the outerlayer comprises HDPE and/or Tecoflex. The inner and outer layers can bethermally fused together in some embodiments. In some embodiments, theinner layer comprises a woven fabric and/or braided filaments such asyarn filaments of PTFE, PET, PEEK, and/or nylon.

Some disclosed expandable sheaths can further include an elastic outercover disposed on an external surface of the outer layer. The elasticouter cover can comprise, for example, heat shrink tubing. Some sheathsinclude one or more radiopaque marker or fillers, such as a C-shapedband positioned between the inner and outer layers near the distal endof the sheath. Some embodiments include a soft tip secured to the distalend of the sheath.

In some embodiments, the inner layer can include at least one foldedportion and at least one weakened portion. A discontinuous outer layercan have an outer surface and an inner surface and a longitudinal gap,and a portion of the inner layer can extend through the longitudinalgap. The at least one folded portion of the inner layer can bepositioned adjacent a portion of the outer surface of the outer layer.In some embodiments, the weakened portion can comprise a score linealong at least a portion of the inner layer and/or a slit along at leasta portion of the inner layer. The weakened portion can be positioned atthe at least one folded portion of the inner layer. In some embodiments,the longitudinal gap can be positioned between a first end and a secondend of the outer layer.

In some embodiments, an expandable sheath can include a hydrophilicinner liner defining a generally horseshoe-shaped lumen therethrough,the inner liner including at least two weakened portions and an elasticcover positioned radially outward of the inner liner. In someembodiments, when the sheath is in the expanded configuration, the innerliner splits apart at the weakened portions so as to form adiscontinuous inner liner.

Methods of making a sheath are also disclosed. One method includesproviding a mandrel having a first diameter, providing a first tubehaving a second diameter, the second diameter being larger than thefirst diameter, mounting the first tube on the mandrel, gathering excessmaterial of the first tube and folding the excess material to one sideto form a folded portion of the inner layer. A second tube can then beprovided, and the second tube can be cut to form a coiled layer. Anadhesive can be applied to at least a portion of the coiled layer andthe coiled layer can be mounted on the first tube such that the adhesiveis positioned between the first tube and the coiled layer. The foldedportion can be lifted in order to position a portion of the coiled layerunder the folded portion.

Some methods include applying heat to the first tube, coiled layer, andmandrel so as to thermally fuse the first tube and the coiled layertogether. In some methods, an elastic outer cover can be secured to theouter surface of the coiled layer. In some methods, a soft tip portioncan be coupled to a distal end of the expandable sheath to facilitatepassing the expandable sheath through a patient's vasculature.

The foregoing and other features and advantages of the invention willbecome more apparent from the following detailed description, whichproceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation view of a sheath according to the presentdisclosure along with an endovascular delivery apparatus for implantinga prosthetic valve.

FIGS. 2A, B, and D are section views of embodiments of a sheath forintroducing a prosthetic device into a patient, and FIG. 2C is aperspective view of one component of such a sheath.

FIG. 3 is an elevation view of the sheath shown in FIG. 2.

FIGS. 4A-4B are elevation views of two embodiments of a sheath accordingto the present disclosure, having varying outer diameters.

FIG. 5 illustrates an elevation view of one embodiment of a sheath,expanded at a first location to accommodate a delivery system.

FIG. 6 shows an elevation view of the sheath of claim 5, expanded at asecond location, farther down the sheath.

FIG. 7 shows a section view of another embodiment of a sheath thatfurther comprises an outer covering or shell.

FIG. 8 illustrates an elevation view of one embodiment of a sheath withan outer covering or shell.

FIG. 9 illustrates a partial elevation view of one embodiment of anintermediate tubular layer that can be used to construct a sheathaccording to the present disclosure.

FIG. 10 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having a variable diamond design.

FIG. 11 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having a diamond design with spring struts.

FIG. 12 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having a diamond design with straight struts.

FIG. 13 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having a saw tooth design with spring struts.

FIG. 14 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having a saw tooth design with straightstruts.

FIG. 15 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having a diamond design with straight struts.

FIG. 16 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having a helical or spiral design.

FIG. 17 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having a diamond design with non-straightstruts.

FIG. 18 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having an alternative diamond design withnon-straight struts.

FIG. 19 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having yet another diamond design withnon-straight struts.

FIG. 20 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having a diamond design with struts.

FIG. 21 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having a design similar to that shown in FIG.20, but with additional struts.

FIG. 22 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having a diamond design with spiral struts.

FIG. 23 illustrates a partial elevation view of another embodiment of anintermediate tubular layer having a diamond design with adjacent struts.

FIG. 24 illustrates a section view of one embodiment of a sheath havinga longitudinal notch.

FIG. 25 shows a section view of one embodiment of a sheath having alongitudinal cut in the inner layer.

FIG. 26 shows a perspective view of one embodiment of a sheath having aplurality of notches or cuts in the outer tubular layer.

FIG. 27A illustrates a section view of one embodiment of a sheath,wherein the outer tubular layer contains a longitudinal cut, and theinner layer extends into the gap created by the cut in the outer tubularlayer, in an unexpanded configuration; and FIGS. 27B-27E show sectionviews of various embodiments of a sheath in the unexpandedconfiguration.

FIG. 28 shows a section view of the sheath of FIG. 27A in an expandedconfiguration.

FIGS. 29A-29D show section views of various embodiments of a sheathhaving overlapping sections.

FIG. 30 illustrates a block diagram of one embodiment of a method ofmaking a sheath according to the present disclosure.

FIG. 31 illustrates a block diagram of another embodiment of a method ofmaking a sheath according to the present disclosure.

FIGS. 32A-32H illustrates section or elevation views of various methodsteps of the methods shown in FIGS. 30-31.

FIG. 33 illustrates a plan view of one embodiment of a sheath having apartial slit or score line.

FIG. 34 illustrates a plan view of another embodiment of a sheath havinga partial slit or score line.

FIG. 35 is an elevation view of an expandable sheath according to thepresent disclosure and a representative housing.

FIG. 36 is an enlarged cutaway view of the distal end of the sheath ofFIG. 35.

FIG. 37 is a section view of the distal end of the sheath of FIG. 35,taken along line 37-37 in FIG. 36.

FIG. 38 is a section view of a proximal section of the sheath of FIG.35, taken along line 38-38 in FIG. 35.

FIG. 39 is a section view of the sheath of FIG. 35 in a rest(unexpanded) configuration, taken along line 39-39 in FIG. 35.

FIG. 40 is the section view of the sheath of FIG. 39, in an expandedconfiguration.

FIG. 41 shows an elevation view of an expandable sheath having anelastic outer cover, according to another embodiment.

FIG. 42 illustrates a section view of the sheath of FIG. 41, taken alongline 42-42 in FIG. 41.

FIG. 43 illustrates the section view of the sheath shown in FIG. 42, inan expanded configuration.

FIG. 44 illustrates a section view of another embodiment of anexpandable sheath.

FIG. 45 shows an expanded configuration of the sheath of FIG. 44.

FIG. 46 illustrates a section view of another embodiment of anexpandable sheath.

FIG. 47 shows an expanded configuration of the sheath of FIG. 46.

FIG. 48 illustrates a section view of another embodiment of anexpandable sheath according to the present disclosure.

FIG. 49 illustrates a section view of another embodiment of anexpandable sheath.

DETAILED DESCRIPTION

As used in this application and in the claims, the singular forms “a,”“an,” and “the” include the plural forms unless the context clearlydictates otherwise. Additionally, the term “includes” means “comprises.”Further, the terms “coupled” and “associated” generally meanselectrically, electromagnetically, and/or physically (e.g., mechanicallyor chemically) coupled or linked and does not exclude the presence ofintermediate elements between the coupled or associated items.

Although the operations of exemplary embodiments of the disclosed methodmay be described in a particular, sequential order for convenientpresentation, it should be understood that disclosed embodiments canencompass an order of operations other than the particular, sequentialorder disclosed. For example, operations described sequentially may insome cases be rearranged or performed concurrently. Further,descriptions and disclosures provided in association with one particularembodiment are not limited to that embodiment, and may be applied to anyembodiment disclosed.

Moreover, for the sake of simplicity, the attached figures may not showthe various ways (readily discernable, based on this disclosure, by oneof ordinary skill in the art) in which the disclosed system, method, andapparatus can be used in combination with other systems, methods, andapparatuses. Additionally, the description sometimes uses terms such as“produce” and “provide” to describe the disclosed method. These termsare high-level abstractions of the actual operations that can beperformed. The actual operations that correspond to these terms can varydepending on the particular implementation and are, based on thisdisclosure, readily discernible by one of ordinary skill in the art.

Disclosed embodiments of an expandable sheath can minimize trauma to thevessel by allowing for temporary expansion of a portion of theintroducer sheath to accommodate the delivery system, followed by areturn to the original diameter once the device passes through. Someembodiments can comprise a sheath with a smaller profile (e.g., asmaller diameter in the rest configuration) than that of prior artintroducer sheaths. Furthermore, present embodiments can reduce thelength of time a procedure takes, as well as reduce the risk of alongitudinal or radial vessel tear, or plaque dislodgement because onlyone sheath is required, rather than several different sizes of sheaths.Embodiments of the present expandable sheath can avoid the need formultiple insertions for the dilation of the vessel. Such expandablesheaths can be useful for many types of minimally invasive surgery, suchas any surgery requiring introduction of an apparatus into a subject'svessel. For example, the sheath can be used to introduce other types ofdelivery apparatus for placing various types of intraluminal devices(e.g., stents, prosthetic heart valves, stented grafts, etc.) into manytypes of vascular and non-vascular body lumens (e.g., veins, arteries,esophagus, ducts of the biliary tree, intestine, urethra, fallopiantube, other endocrine or exocrine ducts, etc.).

FIG. 1 illustrates a sheath 8 according to the present disclosure, inuse with a representative delivery apparatus 10, for delivering aprosthetic device 12, such as a tissue heart valve to a patient. Theapparatus 10 can include a steerable guide catheter 14 (also referred toas a flex catheter), a balloon catheter 16 extending through the guidecatheter 14, and a nose catheter 18 extending through the ballooncatheter 16. The guide catheter 14, the balloon catheter 16, and thenose catheter 18 in the illustrated embodiment are adapted to slidelongitudinally relative to each other to facilitate delivery andpositioning of the valve 12 at an implantation site in a patient's body,as described in detail below. Generally, sheath 8 is inserted into avessel, such as the transfemoral vessel, passing through the skin ofpatient, such that the distal end of the sheath 8 is inserted into thevessel. Sheath 8 can include a hemostasis valve at the opposite,proximal end of the sheath. The delivery apparatus 10 can be insertedinto the sheath 8, and the prosthetic device 12 can then be deliveredand implanted within patient.

FIGS. 2A, 2B, and 2D show section views of embodiments of a sheath 22for use with a delivery apparatus such as that shown in FIG. 1. FIG. 2Cshows a perspective view of one embodiment of an inner layer 24 for usewith the sheath 22. Sheath 22 includes an inner layer, such as innerpolymeric tubular layer 24, an outer layer, such as outer polymerictubular layer 26, and an intermediate tubular layer 28 disposed betweenthe inner and outer polymeric tubular layers 24, 26. The sheath 22defines a lumen 30 through which a delivery apparatus can travel into apatient's vessel in order to deliver, remove, repair, and/or replace aprosthetic device. Such introducer sheaths 22 can also be useful forother types of minimally invasive surgery, such as any surgery requiringintroduction of an apparatus into a subject's vessel. For example, thesheath 22 also can be used to introduce other types of deliveryapparatus for placing various types of intraluminal devices (e.g.,stents, stented grafts, etc.) into many types of vascular andnon-vascular body lumens (e.g., veins, arteries, esophagus, ducts of thebiliary tree, intestine, urethra, fallopian tube, other endocrine orexocrine ducts, etc.).

The outer polymeric tubular layer 26 and the inner polymeric tubularlayer 24 can comprise, for example, PTFE (e.g. Teflon®), polyimide,PEEK, polyurethane, nylon, polyethylene, polyamide, polyether blockamides (e.g. PEBAX®), polyether block ester copolymer, polyesters,fluoropolymers, polyvinyl chloride, thermoset silicone, latex,poly-isoprene rubbers, polyolefin, other medical grade polymers, orcombinations thereof. The intermediate tubular layer 28 can comprise ashape memory alloy such as Nitinol, and/or stainless steel, cobaltchromium, spectra fiber, polyethylene fiber, aramid fiber, orcombinations thereof.

The inner polymeric tubular layer 24 can advantageously be provided witha low coefficient of friction on its inner surface. For example, theinner polymeric tubular layer 24 can have a coefficient of friction ofless than about 0.1. Some embodiments of a sheath 22 can include alubricious liner on the inner surface 32 of the inner polymeric tubularlayer 24. Such a liner can facilitate passage of a delivery apparatusthrough the lumen 30 of the sheath 22. Examples of suitable lubriciousliners include materials that can reduce the coefficient of friction ofthe inner polymeric tubular layer 24, such as PTFE, polyethylene,polyvinylidine fluoride, and combinations thereof. Suitable materialsfor a lubricious liner also include other materials desirably having acoefficient of friction of about 0.1 or less.

The inner diameter of the intermediate tubular layer 28 varies dependingon the application and size of the delivery apparatus and prostheticdevice. In some embodiments, the inner diameter ranges from about 0.005inches to about 0.400 inches. The thickness of the intermediate tubularlayer 28 can be varied depending on the desired amount of radialexpansion, as well as the strength required. For example, the thicknessof the intermediate tubular layer 28 can be from about 0.002 inches toabout 0.025 inches. The thicknesses of the inner polymeric tubular layer24 and the outer polymeric tubular layer 26 can also be varied dependingon the particular application of the sheath 22. In some embodiments, thethickness of the inner polymeric tubular layer 24 ranges from about0.0005 inches to about 0.010 inches, and in one particular embodiment,the thickness is about 0.002 inches. Outer polymeric tubular layers 26can have a thickness of from about 0.002 inches to about 0.015 inches,and in one particular embodiment the outer polymeric tubular layer 26has a thickness of about 0.010 inches.

The hardness of each layer of the sheath 22 can also be varied dependingon the particular application and desired properties of the sheath 22.In some embodiments, the outer polymeric tubular layer 26 has a Shorehardness of from about 25 Durometer to about 75 Durometer.

Additionally, some embodiments of a sheath 22 can include an exteriorhydrophilic coating on the outer surface 34 of the outer polymerictubular layer 26. Such a hydrophilic coating can facilitate insertion ofthe sheath 22 into a patient's vessel. Examples of suitable hydrophiliccoatings include the Harmony™ Advanced Lubricity Coatings and otherAdvanced Hydrophilic Coatings available from SurModics, Inc., EdenPrairie, Minn. DSM medical coatings (available from Koninklijke DSM N.V, Heerlen, the Netherlands), as well as other hydrophilic coatings, arealso suitable for use with the sheath 22.

In some embodiments, the outer surface 34 of the outer polymeric tubularlayer 26 can be modified. For example, surface modifications such asplasma etching can be performed on the outer surface 34. Similarly,other surfaces, both outer and inner, can be surface modified accordingto certain embodiments and desired application. In some embodiments,surface modification can improve adhesion between the layers in theareas of the modification.

The sheath 22 also can have at least one radiopaque filler or marker.The radiopaque filler or marker can be associated with the outer surface34 of the outer polymeric tubular layer 26. Alternatively, theradiopaque filler or marker can be embedded or blended within the outerpolymeric tubular layer 24. Similarly, the radiopaque filler or markercan be associated with a surface of the inner polymeric tubular layer 24or the intermediate tubular layer 28 or embedded within either or bothof those layers.

Suitable materials for use as a radiopaque filler or marker include, forexample, barium sulfite, bismuth trioxide, titanium dioxide, bismuthsubcarbonate, or combinations thereof. The radiopaque filler can bemixed with or embedded in the material used to form the outer polymerictubular layer 26, and can comprise from about 5% to about 45% by weightof the outer polymeric tubular layer. More or less radiopaque materialcan be used in some embodiments, depending on the particularapplication.

In some embodiments, the inner polymeric tubular layer 24 can comprise asubstantially uniform cylindrical tube. In alternative embodiments, theinner polymeric tubular layer 24 can have at least one section ofdiscontinuity along its longitudinal axis to facilitate radial expansionof the inner polymeric tubular layer 24. For example, the innerpolymeric tubular layer 24 can be provided with one or more longitudinalnotches and/or cuts 36 extending along at least a portion of the lengthof the sheath 22. Such notches or cuts 36 can facilitate radialexpansion of the inner polymeric tubular layer 24, thus accommodatingpassage of a delivery apparatus or other device. Such notches and/orcuts 36 can be provided near the inner surface 32, near the outersurface 37, and/or substantially through the entire thickness of theinner polymeric layer 24. In embodiments with a plurality of notchesand/or cuts 36, such notches and/or cuts 36 can be positioned such thatthey are substantially equally spaced from one another circumferentiallyaround the inner polymeric layer 24. Alternatively, notches and cuts 36can be spaced randomly in relation to one another, or in any otherdesired pattern. Some or all of any provided notches and/or cuts 36 canextend longitudinally along substantially the entire length of thesheath 22. Alternatively, some or all of any provided notches and/orcuts 36 can extend longitudinally only along a portion of the length ofthe sheath 22.

As shown in FIGS. 2B and 2C (which illustrates only the inner polymerictubular layer 24), in some embodiments, the inner polymeric tubularlayer 24 contains at least one notch or cut 36 that extendslongitudinally and parallel to an axis defined by the lumen 30,extending substantially the entire length of the sheath 22. Thus, uponintroduction of a delivery apparatus, the inner polymeric tubular layer24 can split open along the notch and/or cut 36 and expand, thusaccommodating the delivery apparatus.

Additionally or alternatively, as shown in FIG. 2D, the outer polymerictubular layer 26 can comprise one or more notches and/or cuts 36.Notches and/or cuts 36, in some embodiments, do not extend through theentire thickness of the outer tubular layer 26. The notches and/or cuts36 can be separable upon radial expansion of the sheath 22. The outerpolymeric tubular layer 26 can be retractable longitudinally, or able tobe pulled back away from the intermediate tubular layer 28 and the innerpolymeric tubular layer 24. In embodiments with a retractable outerpolymeric tubular layer 26, the outer polymeric tubular layer 26 can beretracted to accommodate or facilitate passage of a delivery apparatusthrough the lumen 30, and then can be replaced to its original positionon the sheath 22.

FIG. 3 illustrates an elevation view of the sheath 22 shown in FIG. 2A.In this view, only the outer polymeric tubular layer 26 is visible. Thesheath 22 comprises a proximal end 38 and a distal end 40 opposite theproximal end 38. The sheath 22 can include a hemostasis valve inside thelumen of the sheath 22, at or near the proximal end 38 of the sheath 22.Additionally, the sheath 22 can comprise a soft tip 42 at the distal end40 of the sheath 22. Such a soft tip 42 can be provided with a lowerhardness than the other portions of the sheath 22. In some embodiments,the soft tip 42 can have a Shore hardness from about 25 D to about 40 D.

As shown in FIG. 3, the unexpanded original outer diameter of the sheath22 can be substantially constant across the length of the sheath 22,substantially from the proximal end 38 to the distal end 40. Inalternative embodiments, such as the ones illustrated in FIGS. 4A-4B,the original unexpanded outer diameter of the sheath 22 can decreasefrom the proximal end 38 to the distal end 40. As shown in theembodiment in FIG. 4A, the original unexpanded outer diameter candecrease along a gradient, from the proximal end 38 to the distal end40. In alternative embodiments, such as the one shown in FIG. 4B, theoriginal unexpanded outer diameter of sheath 22 can incrementally stepdown along the length of the sheath 22, wherein the largest originalunexpanded outer diameter is near the proximal end 38 and the smallestoriginal unexpanded outer diameter is near the distal end 40 of thesheath 22.

As shown in FIGS. 5-6, the sheath 22 can be designed to locally expandas the prosthetic device is passed through the lumen of the sheath 22,and then substantially return to its original shape once the prostheticdevice has passed through that portion of the sheath 22. For example,FIG. 5 illustrates a sheath 22 have a localized bulge 44, representativeof a device being passed through the internal lumen of the sheath 22.FIG. 5 shows the device close to the proximal end 38 of the sheath 22,close to the area where the device is introduced into the sheath 22.FIG. 6 shows the sheath 22 of FIG. 5, with the device having progressedfurther along the sheath 22. The localized bulge 44 is now closer to thedistal end 40 of the sheath 22, and thus is about to be introduced to apatient's vessel. As evident from FIGS. 5 and 6, once the localizedbulge associated with the device has passed through a portion of thelumen of the sheath 22, that portion of the sheath 22 can automaticallyreturn to its original shape and size, at least in part due to thematerials and structure of the sheath 22.

The sheath 22 has an unexpanded inner diameter equal to the innerdiameter of the inner polymeric tubular layer (not visible in FIGS.5-6), and an unexpanded outer diameter 46 equal to the outer diameter ofthe outer polymeric tubular layer 26. The sheath 22 is designed to beexpanded to an expanded inner diameter and an expanded outer diameter 48which are larger than the unexpanded inner diameter and the unexpandedouter diameter 46, respectively. In one representative embodiment, theunexpanded inner diameter is about 16 Fr and the unexpanded outerdiameter 46 is about 19 Fr, while the expanded inner diameter is about26 Fr and the expanded outer diameter 48 is about 29 Fr. Differentsheaths 22 can be provided with different expanded and unexpanded innerand outer diameters, depending on the size requirements of the deliveryapparatus for various applications. Additionally, some embodiments canprovide more or less expansion depending on the particular designparameters, the materials, and/or configurations used.

In some embodiments of a sheath according to the present disclosure, andas shown in section in FIG. 7 and in elevation in FIG. 8, the sheath 22can additionally comprise an outer covering, such as outer polymericcovering 50, disposed on the outer surface 52 of the outer polymerictubular layer 26. The outer polymeric covering 50 can provide aprotective covering for the underlying sheath 22. In some embodiments,the outer polymeric covering 50 can contain a self-expandable sheath ina crimped or constrained state, and then release the self-expandablesheath upon removal of the outer polymeric covering 50. For example, insome embodiments of a self-expandable sheath, the intermediate layer 28can comprise Nitinol and/or other shape memory alloys, and theintermediate layer 28 can be crimped or radially compressed to a reduceddiameter within the outer polymeric tubular layer 26 and the outerpolymeric covering 50. Once the self-expandable sheath is at leastpartially inserted into a patient's vessel, the outer polymeric covering50 can be slid back, peeled away, or otherwise at least partiallyremoved from the sheath. To facilitate removal of the outer polymericcovering 50, a portion of the outer polymeric covering 50 can remainoutside the patient's vessel, and that portion can be pulled back orremoved from the sheath to allow the sheath to expand. In someembodiments, substantially the entire outer polymeric covering 50 can beinserted, along with the sheath, into a patient's vessel. In theseembodiments, an external mechanism attached to the outer polymericcovering 50 can be provided, such that the outer polymeric covering canbe at least partially removed from the sheath once the sheath isinserted into a patient's vessel.

Once no longer constrained by the outer polymeric covering 50, theradially compressed intermediate layer 28 can self-expand, causingexpansion of the sheath along the length of the intermediate layer 28.In some embodiments, portions of the sheath can radially collapse, atleast partially returning to the original crimped state, as the sheathis being withdrawn from the vessel after completion of the surgicalprocedure. In some embodiments, such collapse can be facilitated and/orencouraged by an additional device or layer that, in some embodiments,can be mounted onto a portion of the sheath prior to the sheath'sinsertion into the vessel.

The outer polymeric covering 50, in some embodiments, is not adhered tothe other layers of the sheath 22. For example, the outer polymericcovering 50 may be slidable with respect to the underlying sheath, suchthat it can be easily removed or retracted from its initial position onthe sheath 22.

As seen in FIG. 8, the outer polymeric covering 50 can include one ormore peel tabs 54 to facilitate manual removal of the outer polymericcovering 50. The outer polymeric covering 50 can be automatically ormanually retractable and/or splittable to facilitate radial expansion ofthe sheath 22. Peel tabs 54 can be located approximately 90 degrees fromany cut or notch present in the outer polymeric covering 50, andapproximately 180 degrees offset from one another. In alternativeembodiments, the peel tabs 54 can extend substantially around thecircumference of the outer polymeric covering 50, thus resulting in asingle circular peel tab 54.

Suitable materials for the outer polymeric covering 50 are similar tothose materials suitable for the inner polymeric tubular layer and theouter polymeric tubular layer, and can include PTFE and/or high densitypolyethylene.

Turning now to the intermediate tubular layer 28, several differentconfigurations are possible. The intermediate tubular layer 28 isgenerally a thin, hollow, substantially cylindrical tube comprising anarrangement, pattern, structure, or configuration of wires or struts,however other geometries can also be used. The intermediate tubularlayer 28 can extend along substantially the entire length of the sheath22, or alternatively, can extend only along a portion of the length ofsheath 22. Suitable wires can be round, ranging from about 0.0005 inchesthick to about 0.10 inches thick, or flat, ranging from about 0.0005inches×0.003 inches to about 0.003 inches×0.007 inches. However, othergeometries and sizes are also suitable for certain embodiments. Ifbraided wire is used, the braid density can be varied. Some embodimentshave a braid density of from about thirty picks per inch to about eightypicks per inch and can include up to thirty-two wires in various braidpatterns.

One representative embodiment of an intermediate tubular layer comprisesa braided Nitinol composite which is at least partially encapsulated byan inner polymeric tubular member and an outer polymeric tubular memberdisposed on inner and outer surfaces of the intermediate tubular layer,respectively. Such encapsulation by polymeric layers can be accomplishedby, for example, fusing the polymeric layers to the intermediate tubularlayer, or dip coating the intermediate tubular layer. In someembodiments, an inner polymeric tubular member, an intermediate tubularlayer, and an outer polymeric tubular layer can be arranged on amandrel, and the layers can then be thermally fused or melted into oneanother by placing the assembly in an oven or otherwise heating it. Themandrel can then be removed from the resulting sheath. In otherembodiments, dip coating can be used to apply an inner polymeric tubularmember to the surface of a mandrel. The intermediate tubular layer canthen be applied, and the inner polymeric tubular member allowed to cure.The assembly can then be dip coated again, such as to apply a thincoating of, for example, polyurethane, which will become the outerpolymeric tubular member of the sheath. The sheath can then be removedfrom the mandrel.

Additionally, the intermediate tubular layer 28 can be, for example,braided or laser cut to form a pattern or structure, such that theintermediate tubular layer 28 is amenable to radial expansion. FIGS.9-23 illustrate partial elevation views of various structures for theintermediate tubular layer. Some illustrated structures, such as thoseshown in FIGS. 11-14 and 23, include at least one discontinuity. Forexample, the struts 56, 58, 60, 62, 64 shown in FIGS. 11, 12, 13, 14,and 23, respectively, result in a discontinuous intermediate tubularlayer 28 in that the struts 56, 58, 60, 62, 64 separate adjacentsections of the intermediate tubular layer 28 from each other, where thesections are spaced apart from each other along a longitudinal axisparallel to the lumen of the sheath. Thus, the structure of theintermediate tubular layer 28 can vary from section to section, changingalong the length of the sheath.

The structures shown in FIGS. 9-23 are not necessarily drawn to scale.Components and elements of the structures can be used alone or incombination within a single intermediate tubular layer 28. The scope ofthe intermediate tubular layer 28 is not meant to be limited to theseparticular structures; they are merely exemplary embodiments.

Alternative embodiments of a sheath for introducing a prosthetic deviceare also described. For example, FIGS. 24-26 illustrate a section viewand a perspective view, respectively, of a sheath 66 for introducing aprosthetic device into a body. The sheath 66 comprises an inner layer,such as inner polymeric layer 68, an outer layer, such as polymerictubular layer 70, and a hemostasis valve (not shown). The innerpolymeric layer 68 and the outer polymeric tubular layer 70 at leastpartially enclose a lumen 72, through which a delivery apparatus andprosthetic device can pass from outside the patient's body into thepatient's vessel. Either or both of the inner polymeric layer 68 and theouter polymeric layer 70 can be provided with at least one longitudinalnotch and/or cut to facilitate radial expansion of the sheath.

For example, FIG. 24 illustrates a longitudinal notch 74 in the innerpolymeric layer 68 that can facilitate radial expansion of the sheath66. The longitudinal notch 74 can separate or split open completely uponapplication of a radial force due to insertion of a delivery apparatusor prosthetic device. Similarly, FIG. 25 illustrates a longitudinal cut76 in the inner polymeric layer 68 that can also facilitate radialexpansion of the sheath 66. The outer polymeric layer 70 can,additionally or alternatively, comprise one or more longitudinal cuts 76or notches 74. Such cuts and/or notches, whether in the inner polymericlayer 68 or the outer polymeric layer 70, can extend substantiallythrough the entire thickness of the layer, or can extend only partiallythrough the thickness of the layer. The cuts and/or notches can bepositioned at or near the inner or outer surface, or both surfaces, ofthe inner and/or outer polymeric layers 68, 70.

FIG. 26 illustrates a perspective view of one embodiment of an innerpolymeric layer 68 with longitudinal notches 74 and a longitudinal cut76. More or fewer notches 74 and/or cuts 76 can be provided. Forclarity, the outer polymeric layer 70 is not shown in FIG. 26. As shownin FIG. 26, longitudinal notches 74 and/or cuts 76 can extend only alonga portion of the length of sheath 66. In alternative embodiments, one ormore notches 74 and/or cuts 76 can extend substantially along the entirelength of the sheath 66. Additionally, notches 74 and/or cuts 76 can bepositioned randomly or patterned.

One particular embodiment of a sheath 66 comprises a sheath having anotch or cut in the outer polymeric layer 70 or the inner polymericlayer 68 that extends longitudinally along approximately 75% of thelength of the sheath 66. If such a notch or cut extends only partiallythrough the associated layer, it can have a relatively low tear force,such as a tear force of about 0.5 lbs., so that the notch splits openrelatively easily during use.

The inner polymeric layer 68 and the outer polymeric layer 70 canoptionally be adhered together or otherwise physically associated withone another. The amount of adhesion between the inner polymeric layer 68and the outer polymeric layer 70 can be variable over the surfaces ofthe layers. For example, little to no adhesion can be present at areasaround or near any notches and/or cuts present in the layers, so as notto hinder radial expansion of the sheath 66. Adhesion between the layerscan be created by, for example, thermal bonding and/or coatings.Embodiments of a sheath 66 can be formed from an extruded tube, whichcan serve as the inner polymeric layer 68. The inner polymeric layer 68can be surface treated, such as by plasma etching, chemical etching orother suitable methods of surface treatment. By treating the surface ofthe inner polymeric layer 68, the outer surface of the inner polymericlayer 68 can have areas with altered surface angles that can providebetter adhesion between the inner polymeric layer 68 and the outerpolymeric layer 70. The treated inner polymeric layer can be dip coatedin, for example, a polyurethane solution to form the outer polymericlayer 70. In some configurations, the polyurethane may not adhere wellto untreated surface areas of the inner polymeric layer 68. Thus, bysurface treating only surface areas of the inner polymeric layer 68 thatare spaced away from the areas of expansion (e.g. the portion of theinner polymeric layer 68 near notches 74 and/or cuts 76), the outerpolymeric layer 70 can be adhered to some areas of the inner polymericlayer 68, while other areas of the inner polymeric layer 68 remain freeto slide relative to the outer polymeric layer 70, thus allowing forexpansion of the diameter of the sheath 66. Thus, areas around or nearany notches 74 and/or cuts 76 can experience little to no adhesionbetween the layers, while other areas of the inner and outer polymericlayers 68, 70 can be adhesively secured or otherwise physicallyassociated with each other.

As with previously disclosed embodiments, the embodiments illustrated inFIGS. 24-26 can be applied to sheaths having a wide variety of inner andouter diameters. Applications can utilize a sheath of the presentdisclosure with an inner diameter of the inner polymeric layer 68 thatis expandable to an expanded diameter of from about 3 Fr to about 26 Fr.The expanded diameter can vary slightly along the length of the sheath66. For example, the expanded outer diameter at the proximal end of thesheath 66 can range from about 3 Fr to about 28 Fr, while the expandedouter diameter at the distal end of the sheath 66 can range from about 3Fr to about 25 Fr. Embodiments of a sheath 66 can expand to an expandedouter diameter that is from about 10% greater than the originalunexpanded outer diameter to about 100% greater than the originalunexpanded outer diameter.

In some embodiments, the outer diameter of the sheath 66 graduallydecreases from the proximal end of the sheath 66 to the distal end ofthe sheath 66. For example, in one embodiment, the outer diameter cangradually decrease from about 26 Fr at the proximal end to about 18 Frat the distal end. The diameter of the sheath 66 can transitiongradually across substantially the entire length of the sheath 66. Inother embodiments, the transition or reduction of the diameter of thesheath 66 can occur only along a portion of the length of the sheath 66.For example, the transition can occur along a length from the proximalend to the distal end, where the length can range from about 0.5 inchesto about the entire length of sheath 66.

Suitable materials for the inner polymeric layer 68 can have a highelastic strength and include materials discussed in connection withother embodiments, especially Teflon (PTFE), polyethylene (e.g. highdensity polyethylene), fluoropolymers, or combinations thereof. In someembodiments, the inner polymeric layer 68 preferably has a lowcoefficient of friction, such as a coefficient of friction of from about0.01 to about 0.5. Some preferred embodiments of a sheath 66 comprise aninner polymeric layer 68 having a coefficient of friction of about 0.1or less.

Likewise, suitable materials for the outer polymeric layer 70 includematerials discussed in connection with other embodiments, and otherthermoplastic elastomers and/or highly elastic materials.

The Shore hardness of the outer polymeric layer 70 can be varied fordifferent applications and embodiments. Some embodiments include anouter polymeric layer with a Shore hardness of from about 25 A to about80 A, or from about 20 D to about 40 D. One particular embodimentcomprises a readily available polyurethane with a Shore hardness of 72A. Another particular embodiment comprises a polyethylene innerpolymeric layer dipped in polyurethane or silicone to create the outerpolymeric layer.

The sheath 66 can also include a radiopaque filler or marker asdescribed above. In some embodiments, a distinct radiopaque marker orband can be applied to some portion of the sheath 66. For example, aradiopaque marker can be coupled to the inner polymeric layer 68, theouter polymeric layer 70, and/or can be positioned in between the innerand outer polymeric layers 68, 70.

FIGS. 27A-27E and 28 illustrate section views of various embodiments ofunexpanded (FIGS. 27A-27E) and expanded (FIG. 28) sheaths 66 accordingto the present disclosure. The sheath 66 includes a split outerpolymeric tubular layer 70 having a longitudinal cut 76 through thethickness of the outer polymeric tubular layer 70 such that the outerpolymeric tubular layer 70 comprises a first portion 78 and a secondportion 80 separable from one another along the cut 76. An expandableinner polymeric layer 68 is associated with an inner surface 82 of theouter polymeric tubular layer 70, and, in the unexpanded configurationshown in FIG. 27A, a portion of the inner polymeric layer 68 extendsthrough a gap created by the cut 76 and can be compressed between thefirst and second portions 78, 80 of the outer polymeric tubular layer70. Upon expansion of the sheath 66, as shown in FIG. 28, first andsecond portions 78, 80 of the outer polymeric tubular layer 70 haveseparated from one another, and the inner polymeric layer 68 is expandedto a substantially cylindrical tube. In some embodiments, two or morelongitudinal cuts 76 may be provided through the thickness of the outerpolymeric tubular layer 70. In such embodiments, a portion of the innerpolymeric layer 68 may extend through each of the longitudinal cuts 76provided in the outer polymeric tubular layer 70.

Preferably, the inner polymeric layer 68 comprises one or more materialsthat are elastic and amenable to folding and/or pleating. For example,FIG. 27A illustrates an inner polymeric layer 68 with folded regions 85.As seen in FIGS. 27A-27E, the sheath 66 can be provided with one or morefolded regions 85. Such folded regions 85 can be provided along a radialdirection and substantially conform to the circumference of the outerpolymeric tubular layer 70. At least a portion of the folded regions 85can be positioned adjacent the outer surface 83 of the outer polymerictubular layer 70. Additionally, as shown in FIGS. 27B and 27E, at leasta portion of the folded region or regions 85 can be overlapped by anouter covering, such as outer polymeric covering 81. The outer polymericcovering 81 can be adjacent at least a portion of the outer surface 83of the outer polymeric tubular layer 70. The outer polymeric covering 81serves to at least partially contain the folded regions 85 of the innerpolymeric layer 68, and can also prevent the folded regions 85 fromseparating from the outer polymeric tubular layer 70 when, for example,the sheath 66 undergoes bending. In some embodiments, the outerpolymeric covering 81 can be at least partially adhered to the outersurface 83 of the outer polymeric tubular layer 70. The outer polymericcovering 81 can also increase the stiffness and/or durability of thesheath 66. Additionally, as shown in FIGS. 27B and 27E, the outerpolymeric covering 81 may not entirely overlap the circumference of thesheath 66. For example, the outer polymeric covering 81 may be providedwith first and second ends, where the ends do not contact one another.In these embodiments, only a portion of the folded region 85 of theinner polymeric layer 68 is overlapped by the outer polymeric covering81.

In embodiments having a plurality of folded regions 85, the regions canbe equally displaced from each other around the circumference of theouter polymeric tubular layer 70. Alternatively, the folded regions canbe off-center, different sizes, and/or randomly spaced apart from eachother. While portions of the inner polymeric layer 68 and the outertubular layer 70 can be adhered or otherwise coupled to one another, thefolded regions 85 preferably are not adhered or coupled to the outertubular layer 70. For example, adhesion between the inner polymericlayer 68 and the outer tubular layer 70 can be highest in areas ofminimal expansion.

One particular embodiment of the sheath illustrated in FIGS. 27A-28comprises a polyethylene (e.g. high density polyethylene) outerpolymeric tubular layer 70 and a PTFE inner polymeric layer 68. However,other materials are suitable for each layer, as described above.Generally, suitable materials for use with the outer polymeric tubularlayer 70 include materials having a high stiffness or modulus ofstrength that can support expansion and contraction of the innerpolymeric layer 68.

In some embodiments, the outer polymeric tubular layer 70 comprises thesame material or combination of materials along the entire length of theouter polymeric tubular layer 70. In alternative embodiments, thematerial composition can change along the length of the outer polymerictubular layer 70. For example, the outer polymeric tubular layer can beprovided with one or more segments, where the composition changes fromsegment to segment. In one particular embodiment, the Durometer ratingof the composition changes along the length of the outer polymerictubular layer 70 such that segments near the proximal end comprise astiffer material or combination of materials, while segments near thedistal end comprise a softer material or combination of materials. Thiscan allow for a sheath 66 having a relatively stiff proximal end at thepoint of introducing a delivery apparatus, while still having arelatively soft distal tip at the point of entry into the patient'svessel.

As with other disclosed embodiments, the embodiments of sheath 66 shownin FIGS. 27A-28 can be provided in a wide range of sizes and dimensions.For example, the sheath 66 can be provided with an unexpanded innerdiameter of from about 3 Fr to about 26 Fr. In some embodiments, thesheath 66 has an unexpanded inner diameter of from about 15 Fr to about16 Fr. In some embodiments, the unexpanded inner diameter of the sheath66 can range from about 3 Fr to about 26 Fr at or near the distal end ofsheath 66, while the unexpanded inner diameter of the sheath 66 canrange from about 3 Fr to about 28 Fr at or near the proximal end ofsheath 66. For example, in one unexpanded embodiment, the sheath 66 cantransition from an unexpanded inner diameter of about 16 Fr at or nearthe distal end of the sheath 66 to an unexpanded inner diameter of about26 Fr at or near the proximal end of the sheath 66.

The sheath 66 can be provided with an unexpanded outer diameter of fromabout 3 Fr to about 30 Fr, and, in some embodiments has an unexpandedouter diameter of from about 18 Fr to about 19 Fr. In some embodiments,the unexpanded outer diameter of the sheath 66 can range from about 3 Frto about 28 Fr at or near the distal end of sheath 66, while theunexpanded outer diameter of the sheath 66 can range from about 3 Fr toabout 30 Fr at or near the proximal end of sheath 66. For example, inone unexpanded embodiment, the sheath 66 can transition from anunexpanded outer diameter of about 18 Fr at or near the distal end ofthe sheath 66 to an unexpanded outer diameter of about 28 Fr at or nearthe proximal end of the sheath 66.

The thickness of the inner polymeric layer 68 can vary, but in somepreferred embodiments is from about 0.002 inches to about 0.015 inches.In some embodiments, expansion of the sheath 66 can result in expansionof the unexpanded outer diameter of from about 10% or less to about 430%or more.

As with other illustrated and described embodiments, the embodimentsshown in FIGS. 27A-28 can be provided with a radiopaque filler and/or aradiopaque tip marker as described above. The sheath 66 can be providedwith a radiopaque tip marker provided at or near the distal tip of thesheath 66. Such a radiopaque tip marker can comprise materials such asthose suitable for the radiopaque filler, platinum, iridium,platinum/iridium alloys, stainless steel, other biocompatible metals, orcombinations thereof.

FIGS. 29A-29D show section views of other possible configurations of asheath 66 for introducing a prosthetic device into a patient'svasculature. The sheath 66 comprises a polymeric tubular layer 84 havingan inner surface 86 and an outer surface 88. The thickness of thepolymeric tubular layer 84 extends from the inner surface 86 to theouter surface 88. As shown in FIGS. 29B-29D, the polymeric tubular layer84 can be formed with at least a first angular portion 90 of reducedthickness adjacent the inner surface 86 and a second angular portion 92of reduced thickness adjacent the outer surface 88, with the secondportion 92 at least partially overlapping the first portion 90. FIG. 29Aillustrates a similar configuration, where a second portion 92 at leastpartially overlaps a first portion 90 in a partial coil configuration.In the embodiment of FIG. 29A, the second portion 92 and the firstportion 90 can have the same thickness.

In preferred embodiments, the first and second portions 90, 92 are notadhered to one another. In some embodiments, and best seen in FIG. 29A,there can be a small gap 94 between the first and second portions 90, 92that can give the sheath 66 the appearance of having two interior lumens72, 94. FIGS. 29A-29D illustrate the sheath 66 in unexpandedconfigurations. Preferably, upon expansion of the sheath 66, the ends ofthe first and second portions 90, 92 abut or are in close proximity toeach other to reduce or eliminate any gap between them.

In some embodiments, a sheath 66 can comprise a partial slit or scoreline along at least a portion of its length. For example, as shown inFIG. 33, a sheath 66 can comprise an outer polymeric tubular layer 70over an inner polymeric layer 68. The inner polymeric layer can extendthrough a cut in the outer polymeric tubular layer 70, to form a foldedregion 85 on the outer surface of the outer polymeric tubular layer 70,such as also shown in FIG. 27C. The folded region 85 of the inner layer,in some embodiments, terminates before the outer polymeric tubular layer70 (i.e. the outer polymeric tubular layer 70 is longer than the innerlayer). As shown in FIG. 33, in these embodiments, the sheath 66 cancomprise a partial slit or score line 77 that can extend from thetermination (distal end) 75 of the folded region 85 to the distal end 40of the sheath 66. In some embodiments, score line 77 can facilitateexpansion of the sheath 66.

Score line 77 can be substantially centrally located with respect to thefolded region 85. In alternative embodiments, score line 77 can bepositioned in other locations relative to the folded region 85. Also,sheath 66 can comprise one or more score lines 77. For example, as shownin FIG. 34, one or more score lines 77 can be peripherally located withrespect to the folded region 85. The one or more score lines 77 can bepositioned anywhere around the circumference of the outer polymerictubular layer 70. In embodiments comprising a radiopaque marker 69 asseen in FIG. 33, a score line 77 can extend from, for example, thedistal end of the radiopaque marker 69 substantially to the distal end40 of the sheath 66.

FIGS. 35 and 36 illustrate an expandable sheath 100 according to thepresent disclosure, which can be used with a delivery apparatus fordelivering a prosthetic device, such as a tissue heart valve into apatient. In general, the delivery apparatus can include a steerableguide catheter (also referred to as a flex catheter), a balloon catheterextending through the guide catheter, and a nose catheter extendingthrough the balloon catheter (e.g., as depicted in FIG. 1). The guidecatheter, the balloon catheter, and the nose catheter can be adapted toslide longitudinally relative to each other to facilitate delivery andpositioning of the valve at an implantation site in a patient's body.However, it should be noted that the sheath 100 can be used with anytype of elongated delivery apparatus used for implantingballoon-expandable prosthetic valves, self-expanding prosthetic valves,and other prosthetic devices. Generally, sheath 100 can be inserted intoa vessel (e.g., the femoral or iliac arteries) by passing through theskin of patient, such that a soft tip portion 102 at the distal end 104of the sheath 100 is inserted into the vessel. The sheath 100 can alsoinclude a proximal flared end portion 114 to facilitate mating with anintroducer housing 101 and catheters mentioned above (e.g., the proximalflared end portion 114 can provide a compression fit over the housingtip and/or the proximal flared end portion 114 can be secured to thehousing 101 via a nut or other fastening device or by bonding theproximal end of the sheath to the housing). The introducer housing 101can house one or more valves that form a seal around the outer surfaceof the delivery apparatus once inserted through the housing, as known inthe art. The delivery apparatus can be inserted into and through thesheath 100, allowing the prosthetic device to be advanced through thepatient's vasculature and implanted within the patient.

Sheath 100 can include a plurality of layers. For example, sheath 100can include an inner layer 108 and an outer layer 110 disposed aroundthe inner layer 108. The inner layer 108 can define a lumen throughwhich a delivery apparatus can travel into a patient's vessel in orderto deliver, remove, repair, and/or replace a prosthetic device, movingin a direction along the longitudinal axis X. As the prosthetic devicepasses through the sheath 100, the sheath locally expands from a first,resting diameter to a second, expanded diameter to accommodate theprosthetic device. After the prosthetic device passes through aparticular location of the sheath 100, each successive expanded portionor segment of the sheath 100 at least partially returns to the smaller,resting diameter. In this manner, the sheath 100 can be consideredself-expanding, in that it does not require use of a balloon, dilator,and/or obturator to expand.

The inner and outer layers 108, 110 can comprise any suitable materials.Suitable materials for the inner layer 108 includepolytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE),nylon, polyethylene, polyether block amide (e.g., Pebax), and/orcombinations thereof. In one specific embodiment the inner layer 108 cancomprise a lubricious, low-friction, or hydrophilic material, such asPTFE. Such low coefficient of friction materials can facilitate passageof the prosthetic device through the lumen defined by the inner layer108. In some embodiments, the inner layer 108 can have a coefficient offriction of less than about 0.1. Some embodiments of a sheath 100 caninclude a lubricious liner on the inner surface of the inner layer 108.Examples of suitable lubricious liners include materials that canfurther reduce the coefficient of friction of the inner layer 108, suchas PTFE, polyethylene, polyvinylidine fluoride, and combinationsthereof. Suitable materials for a lubricious liner also include othermaterials desirably having a coefficient of friction of about 0.1 orless.

Suitable materials for the outer layer 110 include nylon, polyethylene,Pebax, HDPE, polyurethanes (e.g., Tecoflex), and other medical gradematerials. In one embodiment, the outer layer 110 can comprise highdensity polyethylene (HDPE) and Tecoflex (or other polyurethanematerial) extruded as a composite. In some embodiments, the Tecoflex canact as an adhesive between the inner layer 108 and the outer layer 110and may only be present along a portion of the inner surface of theouter layer 110. Other suitable materials for the inner and outer layersare also disclosed in U.S. Patent Application Publication No.2010/0094392, which is incorporated herein by reference.

Additionally, some embodiments of a sheath 100 can include an exteriorhydrophilic coating on the outer surface of the outer layer 110. Such ahydrophilic coating can facilitate insertion of the sheath 100 into apatient's vessel. Examples of suitable hydrophilic coatings include theHarmony™ Advanced Lubricity Coatings and other Advanced HydrophilicCoatings available from SurModics, Inc., Eden Prairie, Minn. DSM medicalcoatings (available from Koninklijke DSM N. V, Heerlen, theNetherlands), as well as other hydrophilic coatings (e.g., PTFE,polyethylene, polyvinylidine fluoride), are also suitable for use withthe sheath 100.

Best seen in FIG. 36, the soft tip portion 102 can comprise, in someembodiments, low density polyethylene (LDPE) and can be configured tominimize trauma or damage to the patient's vessels as the sheath isnavigated through the vasculature. For example, in some embodiments, thesoft tip portion 102 can be slightly tapered to facilitate passagethrough the vessels. The soft tip portion 102 can be secured to thedistal end 104 of the sheath 100, such as by thermally bonding the softtip portion 102 to the inner and outer layers of the sheath 100. Such asoft tip portion 102 can be provided with a lower hardness than theother portions of the sheath 100. In some embodiments, the soft tip 102can have a Shore hardness from about 25 D to about 40 D. The tip portion102 is configured to be radially expandable to allow a prosthetic deviceto pass through the distal opening of the sheath 100. For example, thetip portion 102 can be formed with a weakened portion, such as anaxially extending score line or perforated line that is configured tosplit and allow the tip portion to expand radially when the prostheticdevice passes through the tip portion (such as shown in the embodimentsof FIGS. 33 and 34).

FIG. 37 shows a cross-section view of the sheath 100 taken near thedistal end 104 of the sheath 100. As shown in FIGS. 36 and 37, thesheath 100 can include at least one radiopaque filler or marker, such asa discontinuous, or C-shaped, band 112 positioned near the distal end104 of the sheath 100. The marker 112 can be associated with the innerand/or outer layers 108, 110 of the sheath 100. For example, as shown inFIG. 37, the marker 112 can be positioned between the inner layer 108and the outer layer 110. In alternative embodiments, the marker 112 canbe associated with the outer surface of the outer layer 110. In someembodiments, the marker 112 can be embedded or blended within the inneror outer layers 108, 110.

The C-shaped band 112 can serve as a radiopaque marker or filler, toenable visibility of the sheath 100 under fluoroscopy during use withina patient. The C-shaped band 112 can comprise any suitable radiopaquematerial, such as barium sulfite, bismuth trioxide, titanium dioxide,bismuth subcarbonate, platinum, iridium, and combinations thereof. Inone specific embodiment, the C-shaped band can comprise 90% platinum and10% iridium. In other embodiments, the marker 112 need not be a C-shapedband. Other shapes, designs, and configurations are possible. Forexample, in some embodiments, the marker 112 can extend around theentire circumference of the sheath 100. In other embodiments, the marker112 can comprise a plurality of small markers spaced around the sheath100.

FIGS. 38 and 39 show additional cross sections taken at different pointsalong the sheath 100. FIG. 38 shows a cross-section of a segment of thesheath near the proximal end 106 of the sheath 100, as indicated by line38-38 in FIG. 35. The sheath 100 at this location can include innerlayer 108 and outer layer 110. At this location, near the proximal endof the sheath, the layers 108, 110 can be substantially tubular, withoutany slits or folded portions in the layers. By contrast, the layers 108,110 at different locations along the sheath 100 (e.g., at the pointindicated by line 39-39 in FIG. 35) can have a different configuration.

As shown in FIG. 39, the inner layer 108 can be arranged to form asubstantially cylindrical lumen 116 therethrough. Inner layer 108 caninclude one or more folded portions 118. In the embodiment shown in FIG.39, inner layer 108 is arranged to have one folded portion 118 that canbe positioned on either side of the inner layer 108. Inner layer 108 canbe continuous, in that there are no breaks, slits, or perforations ininner layer 108. Outer layer 110 can be arranged in an overlappingfashion such that an overlapping portion 120 overlaps at least a part ofthe folded portion 118 of the inner layer 108. As shown in FIG. 39, theoverlapping portion 120 also overlaps an underlying portion 122 of theouter layer 110. The underlying portion 122 can be positioned tounderlie both the overlapping portion 120 of the outer layer 110, aswell as the folded portion 118 of the inner layer 108. Thus, the outerlayer 110 can be discontinuous, in that it includes a slit or a cut inorder to form the overlapping and underlying portions 120, 122. In otherwords, a first edge 124 of the outer layer 110 is spaced apart from asecond edge 126 of the outer layer 110 so as not to form a continuouslayer.

As shown in FIG. 39, the sheath 100 can also include a thin layer ofbonding or adhesive material 128 positioned between the inner and outerlayers 108, 110. In one embodiment, the adhesive material 128 cancomprise a polyurethane material such as Tecoflex. The adhesive material128 can be positioned on an inner surface 130 of at least a portion ofthe outer layer 110 so as to provide adhesion between selected portionsof the inner and outer layers 108, 110. For example, the outer layer 110may only include a Tecoflex layer 128 around the portion of the innersurface 130 that faces the lumen-forming portion of the inner layer 108.In other words, the Tecoflex layer 128 can be positioned so that it doesnot contact the folded portion 118 of the inner layer 108 in someembodiments. In other embodiments, the Tecoflex layer 128 can bepositioned in different configurations as desired for the particularapplication. For example, as shown in FIG. 39, the Tecoflex layer 128can be positioned along the entire inner surface 130 of the outer layer110. In an alternative embodiment, the Tecoflex layer can be applied tothe outer surface of the inner liner 108 instead of the inner surface ofthe outer layer. The Tecoflex layer can be applied to all or selectedportions on the inner layer; for example, the Tecoflex layer can beformed only on the portion of the inner layer that faces thelumen-forming portion of the outer layer and not on the folded portion.The configuration of FIG. 39 allows for radial expansion of the sheath100 as an outwardly directed radial force is applied from within (e.g.,by passing a medical device such as a prosthetic heart valve through thelumen 116). As radial force is applied, the folded portion 118 can atleast partially separate, straighten, and/or unfold, and/or theoverlapping portion 120 and the underlying portion 122 of the outerlayer 110 can slide circumferentially with respect to one another,thereby allowing the diameter of lumen 116 to enlarge.

In this manner, the sheath 100 is configured to expand from a restingconfiguration (FIG. 39) to an expanded configuration shown in FIG. 40.In the expanded configuration, as shown in FIG. 40, an annular gap 132can form between the longitudinal edges of the overlapping portion 120and the underlying portion 122 of the outer layer 110. As the sheath 100expands at a particular location, the overlapping portion 120 of theouter layer 110 can move circumferentially with respect to theunderlying portion 122 as the folded portion 118 of the inner layer 108unfolds. This movement can be facilitated by the use of a low-frictionmaterial for inner layer 108, such as PTFE. Further, the folded portion118 can at least partially separate and/or unfold to accommodate amedical device having a diameter larger than that of lumen 116 in theresting configuration. As shown in FIG. 40, in some embodiments, thefolded portion of the inner layer 108 can completely unfold, so that theinner layer 108 forms a cylindrical tube at the location of the expandedconfiguration.

The sheath 100 can be configured such that it locally expands at aparticular location corresponding to the location of the medical devicealong the length of the lumen 116, and then locally contracts once themedical device has passed that particular location. Thus, a bulge may bevisible, traveling longitudinally along the length of the sheath as amedical device is introduced through the sheath, representing continuouslocal expansion and contraction as the device travels the length of thesheath 100. In some embodiments, each segment of the sheath 100 canlocally contract after removal of any radial outward force such that itregains the original resting diameter of lumen 116. In some embodiments,each segment of the sheath 100 can locally contract after removal of anyradial outward force such that it at least partially returns to theoriginal resting diameter of lumen 116.

The layers 108, 110 of sheath 100 can be configured as shown in FIG. 39along at least a portion of the length of the sheath 100. In someembodiments, the layers 108, 110 can be configured as shown in FIG. 39along the length A (FIG. 35) extending from a location adjacent the softtip portion 102 to a location closer to the proximal end 106 of thesheath 100. In this matter, the sheath is expandable and contractableonly along a portion of the length of the sheath corresponding to lengthA (which typically corresponds to the section of the sheath insertedinto the narrowest section of the patient's vasculature).

FIGS. 41-49 illustrate additional embodiments and variations on thegeneral sheath 100 described above. It is to be understood that thevariations (e.g., materials and alternate configurations) describedabove with reference to FIGS. 35-40 can also apply to the embodimentsshown in FIGS. 41-49. Furthermore, the variations described below withreference to FIGS. 41-49 can also be applied to the sheath described inFIGS. 35-40.

FIGS. 41-43 illustrate a sheath 700 that additionally includes a strainrelief cover, also referred to as an elastic outer cover, or an elasticcover 702 positioned around at least a part of an inner layer 704 andouter layer 706. As shown in FIG. 41, the elastic cover 702 can extendfor a length L along at least a portion of the main body of the sheath700. In some embodiments, the elastic cover 702 can extend from theproximal end 708 of the sheath 700 and towards the distal end 709 of thesheath. In some embodiments, the elastic cover 702 extends only part waydown the length of the sheath 700. In alternate embodiments, the elasticcover 702 can extend to a point adjacent the distal end 709, or canextend all the way to the distal end 709 of sheath 700. Furthermore, theelastic outer cover 702 need not extend all the way to the proximal end708 of the sheath 700. In some embodiments, the elastic outer cover 702may extend only part way towards the proximal end 708. In someembodiments, the longitudinal length L of the elastic cover 702 canrange from about 10 cm to the entire length of the sheath 700.

As shown in FIGS. 42 and 43, the elastic cover 702 can be a continuoustubular layer, without slits or other discontinuities. The elastic cover702 can be positioned to surround the entire circumference of outerlayer 706, and can extend longitudinally along any portion of the lengthof the sheath 700. The elastic outer cover 702 can comprise any pliable,elastic material(s) that expand and contract, preferably with a highexpansion ratio. Preferably, the materials used can include lowdurometer polymers with high elasticity, such as Pebax, polyurethane,silicone, and/or polyisoprene. Materials for the elastic outer cover 702can be selected such that it does not impede expansion of the sheath700. In fact, the elastic outer cover 702 can stretch and expand as thesheath 700 expands, such as by movement of the folded or scored innerliner with respect to itself.

The elastic outer cover 702 can, in some embodiments, provide hemostasis(e.g., prevent blood loss during implantation of the prosthetic device).For example, the elastic outer cover 702 can be sized or configured toform a seal with the patient's artery when inserted, such that blood issubstantially prevented from flowing between the elastic outer cover 702and the vessel wall. The elastic outer cover 702 can be inserted suchthat it passes the arteriotomy. For example, in embodiments where theelastic outer cover 702 does not extend all the way to the distal end709 of the sheath 700, the elastic cover 702 can extend distally farenough such that when the sheath 700 is fully inserted into the patient,at least part of the elastic outer cover extends through the ateriotomoysite.

The elastic outer cover can have a thickness ranging from, for example,about 0.001″ to about 0.010.″ In some embodiments, the outer cover canhave a thickness of from about 0.003″ to about 0.006.″ The elastic outerover can be configured to expand as the sheath expands, as shown in theexpanded configuration in FIG. 43.

FIG. 42 shows a cross-section of the sheath 700 in a restingconfiguration having an inner diameter D₁. FIG. 43 shows a cross-sectionof the sheath 700 in an expanded configuration, having an inner diameterD₂, where D₂ is greater than D₁. Similar to the embodiment of FIGS.35-40, the sheath 700 can include an inner layer 704 having a foldedportion 710, and an outer layer 706 having an overlapping portion 712and an underlying portion 714. The overlapping portion 712 overlaps atleast a portion of the folded portion 710 of the inner layer, and theunderlying portion 714 underlies at least a portion of the foldedportion 710. As shown in FIGS. 42-43, in some embodiments, theoverlapping portion 712 does not overlap the entire folded portion 710of the inner layer 704, and thus a portion of the folded portion 710 canbe directly adjacent to the elastic outer cover 702 in locations wherethe elastic cover 702 is present. In locations where the elastic cover702 is not present, part of the folded portion 710 may be visible fromthe outside of the sheath 700, as seen in FIG. 41. In these embodiments,the sheath 700 can include a longitudinal seam 722 where the overlappingportion 712 terminates at the folded portion 710. In use, the sheath canbe positioned such that the seam 722 is posterior to the point of thesheath that is 180 degrees from the seam 722 (e.g., facing downward inthe view of FIG. 41). The seam 722 can also be seen in FIG. 41, whichshows that the seam 722 need not extend the entire length of the sheath.In some embodiments, the proximal end portion of the sheath includes twolayers without a folded portion (e.g., similar to FIG. 38) while thedistal end portion of the sheath includes two layers with a foldedportion (e.g., similar to FIG. 39). In some embodiments, the seam 722can end at a transition point between portions of the sheath having afolded inner layer and portions of the sheath not having a folded innerlayer.

In some embodiments, the folded portion 710 can include a weakenedportion, such as a longitudinal perforation, score line, and/or slit 716along at least a portion of the length of the inner layer 704. The slit716 can allow for two adjacent ends 718, 720 of the folded portion 710to move relative to one another as the sheath 700 expands to theexpanded configuration shown in FIG. 43. As a device having an outerdiameter device larger than the initial resting inner diameter of thesheath 700 is inserted through the sheath 700, the device can causelocal expansion of the sheath 700 and cause the sheath 700 to expand atthe partial score or split line location 716. The weakened portion 716can extend longitudinally along any portion of the expandable sheath700.

FIGS. 44 and 45 show another embodiment of an expandable sheath 800having an initial diameter in a resting configuration (FIG. 44) and alarger expanded diameter in an expanded configuration (FIG. 45). Thesheath 800 can include an elastic outer cover 802, an inner layer 804,and an outer layer 806. Inner layer 804 can include first and secondfolded portions 808, 810. The folded portions 808, 810 can be arrangedsuch that they fold away from one another in opposite directions aroundthe circumference of the sheath 800. For example, folded portion 808 canbe folded to the right in the view of FIG. 44 and folded portion 810 canbe folded to the left such that they do not overlap one another, butshare a common segment 812 which is part of both folded portions 808,810. In contrast to previous embodiments, the outer layer 806 does notinclude an overlapping portion in this embodiment, but rather has firstand second underlying portions 814, 816, which underlie the first andsecond folded portions 808, 810, respectively. The inner layer 804 canextend through a gap between the ends of the adjacent underlyingportions 814, 816 (e.g., between a first end and a second end ofdiscontinuous outer layer 806).

Each folded portion 808, 810 can include a weakened portion 818, such asa slit, score line, and/or perforation. Weakened portion 818 can allowthe expandable sheath 800 to expand easily without a high radial force.As the sheath 800 expands, segment 812 along the top of the foldedportions 808, 810 of inner layer 804 can be configured to split apartfrom the rest of the folded portions 808, 810 and the first and secondunderlying portions 814, 816 can move away from one another so as tocreate an enlarged lumen within the inner layer 804. Weakened portions818 can allow for the segment 812 to easily split apart from the innerlayer 804 as the sheath 800 expands.

FIGS. 46-47 show another embodiment of an expandable sheath 900. Sheath900 can be provided with an inner layer 902 and an elastic cover 904surrounding the inner layer 902. While not shown, sheath 900 canadditionally include an intermediate layer positioned between the innerlayer 902 and the elastic cover 904. If present, the intermediate layercan closely follow the contour of the inner layer 902.

Inner layer 902 can be shaped to include one or more folded portions 906arranged to form a generally horseshoe-shaped lumen 908 that extendslongitudinally through sheath 900 along the inner surface of the innerlayer 902. The folded portions 906 can be arranged to form an area 910positioned with the lumen 908 and radially inward from the elastic cover904. In some embodiments, the area 910 can include one or more voids(e.g., smaller lumens or openings extending through portion 910). Insome embodiments, the area 910 can be filled with material (e.g., HDPE)reflowed from an intermediate layer while the sheath is being made. Insome embodiments, the area 910 can be filled with material reflowed fromthe elastic cover 904 during the sheath manufacturing process.

The inner layer 902 can include one or more weakened portions 912, suchas score lines, perforations, or slits. The weakened portions 912 can beconfigured to split apart, separate, or widen as the sheath expands fromits initial resting configuration (FIG. 46) to an expanded configuration(FIG. 47) in the presence of a radial force. As the sheath 900 expands,material from the area 910 can cover any gaps 914 formed at the weakenedportions 912, thereby keeping the lumen 908 substantially sealed.

FIG. 48 shows another embodiment of an expandable sheath 1000 having aninner layer 1002 and a discontinuous outer layer 1004. Sheath 1000 issimilar to the sheath 800 of FIG. 44, except that sheath 1000 is shownwithout an elastic outer cover and further, the inner layer 1002 iscontinuous, without weakened portions at the folds 1006. As shown inFIG. 48, the inner layer 1002 can be configured to have one or morefolds 1006 (e.g., two folds positioned on the outer surface of the outerlayer 1004), with portions 1008 of the outer layer 1004 extendingbetween the folds 1006 and the outer surface 1010 of the inner layer1002 underlying the folds 1006.

FIG. 49 shows yet another embodiment of an expandable sheath 1100 havingan inner layer 1102 and an outer layer 1104. The sheath 1100 is similarto the sheath 100 shown in FIG. 39 in that the inner layer 1102 can becontinuous with a folded portion 1106, and the outer layer 1104 can bediscontinuous with an overlapping portion 1108 overlapping at least apart of the folded portion 1106 and an underlying portion 1110underlying at least a part of the folded portion 1106. The underlyingportion 1110 can thus be positioned between an outer surface 1112 of thelumen-forming portion of the inner layer 1102 and the folded portion1106.

The inner layers 1002, 1102 of the sheaths 1000, 1100, respectively, ofFIGS. 48-49 can be optimized to perform slightly differently than theinner layers of sheaths described above. For example, differentmaterials can be used for the inner liner to increase durability andsoftness of the seam (although such materials can also be used with theother embodiments of expandable sheaths described above). For example,materials such as woven fabrics or braid filaments can be used. Suchfabrics, filaments, or yarns can comprise, for example, PTFE, PET, PEEK,and/or nylon yarns or filaments. These materials can advantageouslyprovide a soft and flexible layer that can be easily formed into thedesired shapes or folded portions. Additionally, such materials canwithstand high temperatures, as well as can possess high tensilestrength and tear resistance. Nonetheless, these materials can also beelastic, experience minimal kinking, and provide soft distal edges forless traumatic insertion into a patient's vessels.

Various methods can be used to produce the sheaths discussed above andbelow, throughout the present disclosure. For example, a method ofmaking the sheath shown in FIGS. 2A-2D can comprise providing a mandreland applying an inner layer on the mandrel, such as by spray coating ordip coating the mandrel. An intermediate layer, such as a meshstructure, can then be mounted on the inner layer. An outer layer can beapplied over the intermediate layer, such as by a second spray coatingor dip coating step. Methods can comprise etching or surface treating atleast a portion of the inner layer. Also, methods can comprise providingone or more notches and/or cuts in the inner layer and/or the outerlayer. Cuts and/or notches can be provided by, for example, lasercutting or etching one or more layers.

In some embodiments of methods of making a sheath such as the sheathsillustrated in FIGS. 2A-2D, layers can be pre-formed and mounted on amandrel, and then fused or thermally bonded together. For example, inone method, an inner layer is applied to a mandrel. An intermediatelayer can be applied to the outer surface of the inner layer. An outerlayer can be applied to the outer surface of the intermediate layer.Heat shrink tubing can be applied, and the assembly heated, such thatthe inner layer, the intermediate layer, and/or the outer layer arethermally bonded and compressed together under the heat shrink tubing.

FIG. 30 illustrates a block diagram of one method of producing a sheathfor use with a delivery apparatus in minimally invasive surgery. One ormore mandrels can be provided (step 300). The mandrel can be providedwith an exterior coating, such as a Teflon® coating, and the mandrel'sdiameter can be predetermined, based on the desired size of theresulting sheath. A liner that will become the inner polymeric layer ofthe sheath, such as a PTFE or high density polyethylene liner, can bemounted on the mandrel (step 302). The liner can be etched and/orsurface treated prior to being mounted on the mandrel, according toconventional etching and surface treatment methods. FIG. 32A illustratesa section view of a sheath at steps 300 and 302 of FIG. 30. A coatedmandrel 96 is inserted within the lumen 72 of the inner polymeric layer68. The circumference of the inner polymeric layer 68 is larger than thecircumference of the mandrel 96, such that an excess portion of theinner polymeric layer 68 can be gathered above the mandrel 96.

A layer of material that will become the outer polymeric tubular layer,such as a layer comprising polyurethane or polyolefin, can be cut ornotched through all, substantially all, or a part of the thickness ofthe layer (step 304). Such a cut or notch can extend longitudinallyalong the length of the layer and can extend along substantially theentire length of the outer polymeric tubular layer. In alternativeembodiments, the cut or notch can be provided along only a portion ofthe outer polymeric tubular layer. For example, the outer polymerictubular layer can be cut starting at the distal end of the outerpolymeric tubular layer, with the cut ending before the proximal end ofthe outer polymeric tubular layer. In one embodiment, the cut can end ata transition, where the outer diameter of the outer polymeric tubularlayer increases or decreases. In one specific embodiment, the cut ornotch can extend longitudinally along about 75% of the length of thesheath.

The cut or notched outer polymeric tubular layer can be applied,positioned, adhered, mounted, thermally fused or bonded, dip coated,and/or otherwise coupled to the etched inner liner (step 306). FIG. 32Bshows a section view of the sheath at step 306 of FIG. 30, with outerpolymeric tubular layer 70 applied to the inner polymeric layer 68 suchthat a portion of the inner polymeric layer 68 extends between the cutformed between first and second portions 78, 80 of the outer polymerictubular layer 70.

In alternative embodiments, the outer polymeric tubular layer can benotched or cut after being mounted on the inner liner/mandrel assembly.The outer polymeric tubular layer can optionally be provided with ahydrophilic coating and/or provided with additional layers, such asbeing dip coated with polyurethane. Some portion of the inner liner canprotrude through the cut in the outer polymeric tubular layer after suchouter polymeric tubular layer is mounted onto the inner liner/mandrelarrangement. Using, for example, a split tool, the protruding portion ofthe inner liner can be folded down onto the outer surface of the outerpolymeric tubular layer (step 308). In some embodiments, the protrudingportion of the inner liner is folded down along the entire length of theresulting sheath, while in other embodiments, the protruding portion ofthe inner liner is only present along a portion of the length of thesheath, or is only folded down along a portion of the length of theresulting sheath. FIG. 32C shows a section view of the sheath at step308 of FIG. 30. A split tool 98 is used to fold the excess portion ofinner polymeric layer 68 over a portion of the outer surface 83 of theouter polymeric tubular layer 70. FIG. 32D shows a section view of thesheath after completion of step 308 of FIG. 30. Split tool 98 has beenremoved, and folding of the excess portion of the inner polymeric layer68 has been completed. FIG. 32E shows a section view of an outercovering, such as outer polymeric covering 99, that can be applied suchthat it overlaps a portion of the folded portion of inner polymericlayer 68. The outer polymeric covering 99 contacts at least a portion ofthe outer surface 83 of the outer polymeric tubular layer 70.

A soft, atraumatic tip can be provided at the distal end of theresulting sheath (step 310). Additional outer layers can also beapplied, if desired. Then, a layer of heat shrink tubing, such asfluorinated ethylene propylene (FEP) heat shrink tubing, can bepositioned over the entire assembly (step 312). An appropriate amount ofheat is applied, thus shrinking the heat shrink tubing and compressingthe layers of the sheath together, such that components of the sheathcan be thermally bonded or fused together where desired. Once thecomponents of the sheath have been bonded together, the heat shrinktubing can be removed (step 314). Finally, the proximal end of thesheath can be adhered or otherwise attached to a housing of a catheterassembly, and the sheath can be removed from the mandrel (step 316).

FIG. 31 illustrates a block diagram of an alternative embodiment of amethod of making a sheath. An inner liner, such as an etched PTFE tubingcan be applied to a tapered mandrel, such as a 16 Fr tapered mandrel,and trimmed to an appropriate length (step 200). A second mandrel, suchas a 0.070 inches diameter mandrel, can be inserted in the lumen of theinner liner such that the mandrels are arranged side by side in theinner liner (step 202). FIG. 32F shows a section view of a sheath atsteps 200 and 202 of FIG. 31. An inner liner or inner polymeric layer 68is applied on a first, tapered, mandrel 96. A second mandrel 97 isinserted into the lumen 72 of the inner polymeric layer 68 created bythe excess portion of the inner polymeric layer 68, as described.

A notched or cut outer polymeric tubular layer, such as high densitypolyethylene tubing that has been notched or cut longitudinally, can beslid onto the tapered mandrel and a portion of the inner liner, startingat the distal end of the tapered mandrel (step 204). The second mandrelcan then be removed (step 206). FIG. 32G illustrates a perspective viewof the sheath at steps 204 and 206 of FIG. 31. A polymeric outer tubularlayer 70 having a longitudinal cut is applied over the tapered mandrel96 and inner polymeric layer 68. The outer tubular layer conforms to theportion of the inner polymeric layer around the tapered mandrel 96, andthe portion of the inner polymeric layer 68 around the second mandrel 97extends through the longitudinal cut in the outer polymeric tubularlayer 70.

A split tool can be inserted into the portion of the lumen of the innerliner that was previously occupied by the second mandrel (step 208). Thesplit tool can then be used to form folds and/or pleats in the excessportion of the inner liner which now extends through the longitudinalcut in the outer polymeric tubular layer (step 210). A radiopaque markerband can optionally be applied at the distal end of the sheath (step212). Heat shrink tubing, such as FEP heat shrink tubing, can be appliedover the entire sheath, and heat can be applied to compress thecomponents of the sheath and bond or fuse them together (step 214). Thesplit tool, heat shrink tubing, and second mandrel can then be removed(step 216). The sheath can then be utilized with a delivery apparatus,such as by bonding the proximal end of the sheath to a polycarbonatehousing of a delivery apparatus or catheter assembly (step 218).

FIG. 32H illustrates an elevation view of the sheath at step 218 of FIG.31. The sheath 66, made according to described methods and processes,can be attached or bonded to a housing 101, such as by bonding theproximal end of the sheath 66 to the polycarbonate housing 101.

In another example, disclosed expandable sheaths can be made using areflowed mandrel process. A mandrel can be provided, with the size ofthe mandrel defining the inner diameter of the sheath lumen in itsresting configuration. A tube of material, such as a PTFE tube that willbecome the sheath's inner liner, can be provided with an inner diametergreater than that of the mandrel (e.g., a 9 mm PTFE tube can be mountedon a 6 mm mandrel). The PTFE tube can be mounted on the mandrel andprepared into the final folded configuration by folding the excessmaterial of the PTFE tube over to one or both sides. An HDPE tube thatwill serve as the outer layer can then be placed over the PTFE liner.The two layer assembly can then be thermally fused together. Forexample, a reflow process can be performed where the assembly is heatedto a temperature high enough such that the inner and/or outer layers areat least partially melted and are then fused together as the heat isremoved and the assembly cools.

An elastic cover can be placed over at least part of the fused layers(e.g., over a proximal section of the sheath) and held in place using athermal process. In some embodiments, the same thermal process can bondthe layers of the sheath and the elastic cover. In other embodiments, afirst thermal process can be used to fuse the layers of the sheath, anda second thermal process can be used to secure the elastic cover to thesheath. In some embodiments, the elastic cover can be heat shrink tubingthat is applied over the expandable sheath, and heated to a temperaturehigh enough to cause the tubing to shrink around the sheath. In someembodiments, a distal soft tip can then be attached to the shaft of theexpandable sheath.

In some embodiments, the outer layer can be co-extruded with an adhesivelayer, such as a layer formed from Tecoflex, such that the Tecoflex ispositioned on an inner surface of the outer layer—in this manner theTecoflex will be positioned between the inner and outer layers in thecompleted sheath. In these embodiments, an HDPE tube can be providedwith a coating of Tecoflex on the inner surface. The HDPE tube can beslit along the length of the tube to open and flatten it, and then cutusing a template in some embodiments. For example, for specificapplications, portions of the outer layer can be cut and removed using atemplate. The cut HDPE can then be placed on the inner layer on themandrel. In some embodiments, only a portion of the outer layer willhave the adhesive Tecoflex. In these embodiments, the sections withoutTecoflex will only be partially fused to the inner layer. In someembodiments, the entire inner surface of the outer layer will have theTecoflex, and the inner surface of the outer layer can be positioned sothat it contacts the inner layer on the mandrel. To position the innerand outer layers as shown in the sheath of FIG. 39, the folded portionof the inner layer can be lifted up, and an edge of the outer layer canbe tucked beneath the fold.

Sheaths of the present disclosure can be used with various methods ofintroducing a prosthetic device into a patient's vasculature. One suchmethod comprises positioning an expandable sheath in a patient's vessel,passing a device through the introducer sheath, which causes a portionof the sheath surrounding the device to expand and accommodate theprofile of the device, and automatically retracting the expanded portionof the sheath to its original size after the device has passed throughthe expanded portion. In some methods, the expandable sheath can besutured to the patient's skin at the insertion site so that once thesheath is inserted the proper distance within the patient's vasculature,it does not move once the implantable device starts to travel throughthe sheath.

Disclosed embodiments of an expandable sheath can be used with otherdelivery and minimally invasive surgical components, such as anintroducer and loader. In one embodiment, the expandable sheath can beflushed to purge any air within the sheath, using, for example, flushport 103 (FIG. 35). An introducer can be inserted into the expandablesheath and the introducer/sheath combination can be fully inserted intovasculature over a guiding device, such as a 0.35″ guidewire.Preferably, the seam formed by the intersection of the folded portion ofthe inner layer and the overlapping portion of the outer layer can bepositioned such it is oriented downward (posterior). Once the sheath andintroducer are fully inserted into a patient's vasculature, in someembodiments, the expandable sheath can be sutured in place at theinsertion site. In this manner, the expandable sheath can besubstantially prevented from moving once positioned within the patient.

The introducer can then be removed and a medical device, such as atranscatheter heart valve can be inserted into the sheath, in someinstances using a loader. Such methods can additionally comprise placingthe tissue heart valve in a crimped state on the distal end portion ofan elongated delivery apparatus, and inserting the elongated deliverydevice with the crimped valve into and through the expandable sheath.Next, the delivery apparatus can be advanced through the patient'svasculature to the treatment site, where the valve can be implanted.

Typically, the medical device has a greater outer diameter than thediameter of the sheath in its original configuration. The medical devicecan be advanced through the expandable sheath towards the implantationsite, and the expandable sheath can locally expand to accommodate themedical device as the device passes through. The radial force exerted bythe medical device can be sufficient to locally expand the sheath to anexpanded diameter (e.g., the expanded configuration) just in the areawhere the medical device is currently located. Once the medical devicepasses a particular location of the sheath, the sheath can at leastpartially contract to the smaller diameter of its originalconfiguration. The expandable sheath can thus be expanded without theuse of inflatable balloons or other dilators. Once the medical device isimplanted, the sheath and any sutures holding in place can be removed.In some embodiments, it is preferable to remove the sheath withoutrotating it.

In view of the many possible embodiments to which the principles of thedisclosed invention can be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope and spirit ofthese claims.

We claim:
 1. A sheath for delivering a medical device, the sheathcomprising: a continuous inner layer defining a lumen having alongitudinal axis and including a first folded region and a secondfolded region and an overlapping portion extending between the first andsecond folded regions; an elastic outer cover extending around the innerlayer and exerting a radially inward force on the inner layer; and adiscontinuous outer layer extending at least partially around the innerlayer and under the elastic outer cover and comprising a first end and asecond end; wherein the first folded region is configured to move closerto the second folded region to shorten the overlapping portion at alocal axial location during application of a radial outward force bypassage of the medical device and wherein shortening of the overlappingportion corresponds with a local expansion of the lumen.
 2. The sheathof claim 1, wherein the first folded region is configured to movefurther away from the second folded region to lengthen the overlappingportion at the local axial location after removal of the radial outwardforce and wherein lengthening of the overlapping portion correspondswith a local contraction of the lumen.
 3. The sheath of claim 2, whereinthe first folded region and the second folded region arecircumferentially spaced from each other.
 4. The sheath of claim 3,wherein the overlapping portion extends circumferentially between thefirst and second folded regions.
 5. The sheath of claim 1, wherein theoverlapping portion is radially spaced from an outer surface of anon-overlapping portion of the inner layer.
 6. The sheath of claim 5,wherein the discontinuous outer layer comprises an underlying portionradially spacing the overlapping portion away from the outer surface ofthe non-overlapping portion.
 7. The sheath of claim 1, wherein, at aproximal end of the sheath, the inner layer has a substantially tubular,unfolded cross-section.
 8. The sheath of claim 1, wherein the first endand second end are spaced apart from each other.
 9. The sheath of claim1, wherein the first and second folded regions are configured to meetand eliminate the overlapping portion at the local axial location. 10.The sheath of claim 9, wherein the inner layer is configured to expandat the local axial location into a substantially tubular, unfoldedcross-section.
 11. A method of delivering a medical device through asheath, the method comprising: introducing the medical device into aproximal end of an elongate lumen defined by a continuous inner layer ofthe sheath; advancing the medical device through the lumen along an axisof the lumen and toward a distal end of the lumen; and locally expandingthe lumen of the sheath at a local axial location while advancing themedical device through the local location; wherein locally expanding thelumen includes moving a first folded region of the inner layer closer toa second folded region of the inner layer and shortening an overlappingportion of the inner layer; and wherein locally expanding the lumenincludes locally expanding a discontinuous outer layer that extends atleast partially around the inner layer and under an elastic outer coverand comprises a first end and a second end.
 12. The method of claim 11,further comprising contracting the lumen of the sheath at the localaxial location by moving the first folded region of the inner layerfurther from the second folded region and lengthening the overlappingportion of the inner layer.
 13. The method of claim 12, whereincontracting the lumen includes radially compressing the inner layer witha radially inward bias of the elastic outer cover extending around theinner layer.
 14. The method of claim 13, wherein locally expanding thelumen further includes expanding against the radially inward bias of theelastic outer cover.
 15. The method of claim 12, wherein contracting thelumen includes progressively contracting the lumen while advancing themedical device distal of the local axial location.
 16. The method ofclaim 11, wherein locally expanding the lumen further includes movingthe first folded region into the second folded region and eliminatingthe overlapping portion of the inner layer.
 17. The method of claim 16,wherein locally expanding the lumen further includes forming the innerlayer into a substantially tubular, unfolded cross-section at the localaxial location.
 18. The method of claim 17, wherein moving the firstfolded region closer to the second folded region includes moving thefolded regions circumferentially toward each other.